Good point...
Firstly I think we modify our bikes for very different reasons.
I am a mixture of maybe three...
Firstly, many of my changes happened as the original parts broke or wore down. I am on a budget always as I have other priories. Anyway, I shop around and find a balance of value and quality. I always buy the best I can afford, and am not afraid of used parts.
Secondly, I change my bike depending on my mood. I go through different stages with wants and needs relating to my bike, which makes a Hybrid sooooo good. Easy for me to go road / trail / mountain easily and cheaply.
Thirdly, I think it's OK to spoil yourself sometimes. For me, within reason. I have a desire for American companies in relation to my MTB / Hybrid needs. Hence my mixture of Cannondale (yes mine is American) and Thomson. If I had the money, I'd include Chris King.
My changes are a combination of the above.
Those of you who've been on bike forums for the past 8 years or so, have seen it with poka dots, red cables etc. The black tie is my current stage. Currently, its set for light trails and mountainous road rides. ie. The single narrow / wide Raceface front chainring (34) and road rear cassette. (11 - 28)
Weight is 11kg but can be quickly lightened with it's SPD-SL pedals and it's 23mm Rubino Pro Slicks which are sitting in the garage when I change my mode again.